The goal of this project is the development of methods for the specific isolation of immune cells, particularly for antigen-reactive cells involved in cellular immune reactions, and for their subcellular fractionation in order to study the mechanisms involved in the development of immune reactivities and immune macromolecules. Antigen-reactive hymphocytes (ARC) are obtained from the spleens of normal mice and from mice immunized with allogeneic tumor cells and normal cells. Spleen cell suspensions containing ARC are incubated with allogeneic and syngeneic target cells attached to insoluble supports. The nonadherent cells are tested for depletion of cytotoxic activity by measurement of Cr51 release from target cells. Graft-versus-host (GVH) activity is measured by the Simonsen spleen weight assay in neonatal mice.